Property Value

The plus sign and minus sign buttons appear next to the root tree nodes only if the ShowRootLines property value is true. If the plus sign and minus sign buttons are not displayed, no visual cue exists to indicate that the tree node contains child tree nodes and is expandable. The user then must double-click a tree node to determine whether it contains child tree nodes, to expand it, or to collapse it.

The following code example illustrates a customized TreeView. By inheriting the TreeView class, this custom version has all the functionality of a typical TreeView. Changing various property values in the constructor provides a unique appearance. Because the ShowPlusMinus property is set to false, the customized control also overrides the OnAfterSelect method so that nodes can be expanded and collapsed when they are clicked.

A control that is customized in this way can be used throughout an organization, making it easy to provide a consistent interface without requiring the control properties to be specified in each individual project.

public class CustomizedTreeView extends TreeView
{
public CustomizedTreeView()
{
// Customize the TreeView control by setting various properties.
set_BackColor(System.Drawing.Color.get_CadetBlue());
set_FullRowSelect(true);
set_HotTracking(true);
set_Indent(34);
set_ShowPlusMinus(false);
// The ShowLines property must be false for the FullRowSelect
// property to work.
set_ShowLines(false);
} //CustomizedTreeView
protected void OnAfterSelect(TreeViewEventArgs e)
{
// Confirm that the user initiated the selection.
// This prevents the first node from expanding when it is
// automatically selected during the initialization of
// the TreeView control.
if (!(e.get_Action().Equals(TreeViewAction.Unknown))) {
if (e.get_Node().get_IsExpanded()) {
e.get_Node().Collapse();
}
else {
e.get_Node().Expand();
}
}
// Remove the selection. This allows the same node to be
// clicked twice in succession to toggle the expansion state.
set_SelectedNode(null);
} //OnAfterSelect
}//CustomizedTreeView